1. Field of the Invention
The present invention relates to the acquisition of underwater aggregates, and more particularly to an apparatus for use in gathering and collecting nodules from the ocean floor and for use in dredging in either deep or shallow water. Collecting nodules from the ocean floor is commonly referred to as "ocean mining".
2. Description of the Prior Art
It has long been known that available minerals exist on the ocean floor in the form of ferromanganese nodules. These are relatively small aggregated lumps of minerals, usually including copper, nickel and cobalt, which are found over large extents of the ocean floor, frequently at depths of 12,000 to 16,000 feet. With the growing scarcity of natural resources, these undersea mineral deposits have attracted an increasing amount of attention. And, because of the rising cost of these minerals, their mining is now considered economically feasible.
Over the last decade, many patents have issued on systems for mining these undersea mineral deposits. For the most part, these systems have included a generally vertical conduit which moves along the ocean floor sucking upwardly the minerals along with a large amount of water. Again, for the most part, these systems have not proven to be fully satisfactory.
Presently, the system that offers an excellent chance of success is one having an endless loop to which is attached a number of buckets. The loop is paid out from a surface vessel, sent to the ocean bottom and then retrieved by the same surface vessel in a vertical conveyor-belt manner. One such system is shown in U.S. Pat. No. 3,672,079, for example.
While the continuous bucket system offers promise, there are certain problems which have prevented its adoption for commercial mining operations. A major problem is that of the descending and ascending portions of the loop becoming entangled. Another problem has been the developement of an appropriate loop structure which will prove reliable in a relatively hostile undersea environment. Still another problem is the development of an appropriate bucket size and configuration so that the mineral-gathering operation can be optimized.
Dredging has also proven to be a problem, eespecially in deep water. Present dredging systems have been relatively inflexible and therefore limited to a working depth of some 50-60 feet. Today there is a need for deep sea dredging to depths of 150-160 feet in order to accommodate the new and huge supertankers presently being used and built. Today, supertankers must load and unload at an offshore facility because the draft of the vessels is too large to be accommodated in most harbors. In certain areas, even such offshore activity is difficult. For example, off Louisiana and Texas, the U.S. continental shelf extends for more than 100 miles, and it is not uncommon for the water depth to be less than 150 feet as far as 50 miles from land. For a ship having a draft of 150 feet, a deep channel must be provided to allow the ship to approach anywhere near land. Because of this dredging depth, existing dredge systems are unworkable due to the high induced stresses such a system would face. Even in relatively shallow water, overstressing of the dredge system is not uncommon.